The present invention is related to an antenna, and more particularly to an antenna adapted to operate internally in an electronic device.
The size of wireless handheld communication devices, such as cellular telephones, is being driven by the marketplace towards smaller and smaller sizes. Consumer and user demand has continued to push a dramatic reduction in the size of communication devices. As these devices become less bulky, users face an increasing number of options for carrying and using the device. For example, portable devices are thin and light enough to be easily carried in a shirt pocket. However, the antennas of such devices, when implemented externally to the device, are prone to damage. Therefore, internal antennas have been developed. However, such internal antenna systems still need to properly operate over multiple frequency bands and with various existing cellular system operating modes. In many cases, network operators providing services on one particular band have had to provide service on a separate band to accommodate its customers. For example, network operators providing service on the DAMPS communication system at 800 MHz and Global System of Mobile (GSM) communication system in a 900 MHz frequency band have had to also rely on operating on the Digital Communication System (DCS) at an 1800 MHz frequency band. Accordingly, wireless communication devices, such as cellular radiotelephones, must be able to communicate at these frequencies, or possibly a fourth frequency spectrum, such as the Personal Communication System (PCS) 1900 MHz. Moreover, in order to operate efficiently, internal antennas require a certain amount of mechanical space to be placed within the device, which becomes difficult with the shrinking geometry of portable devices.
Another serious problem arises in small devices when a user holds the device in their hands, and subsequently over the antenna, which severely degrades antenna efficiency. An extendable antenna shaft would solve part of the problem and provide improved efficiency for the communication device to properly operate at various frequencies. Unfortunately, extendable antennas are still relatively bulky when considering a phone that will possibly be reduced to a credit-card size. In particular, keeping the antenna shaft mechanically rugged for a small phone would be difficult to achieve. Moreover, due to the existing and future size reductions of phones, any extendable or rigid antenna shaft would necessarily be prone to damage.
The need for enhanced operability of communication devices along with the drive to smaller sizes results in conflicting technical requirements for the antenna. Different operational parameters dictate different antenna solutions and implementation schemes for different operating modes. In addition, consumers do not want to operate extendable antennas and do not want a phone prone to damage. In particular, external antennas are susceptible to flex stresses that can occur when carrying the device in a wallet, purse, pants pocket or shirt pocket during even mild user activities such as bending, walking, and sitting.
A recent solution has been to enclose the antenna completely within the housing of the communication device. However, this has required making the device housing larger to accommodate the antenna. Further, the antenna has been located closer to the electronics of the device. As a result, size has increased, efficiency has decreased, and interference has become an issue. Moreover, the requirement to operate at two or more frequencies creates further problems.
Accordingly, there is a need for an internal antenna system that is not prone to damage, does not significantly increase the size of the communication device, and is not located next to the electronics of the communication device. It would also be advantageous to provide the antenna structure in a compact, low-cost implementation structure. Further, it would be of benefit to provide multi-frequency operation of the antenna.